Method for the separation and recovery of krypton and xenon from gaseous mixtures containing them



Oct. 13,v 1936. c, g, VAN uys 2,057,459

METHOD FOR THE SEPARATION AND RECOVERY OF KRYP'I'ON AND XENON FROM GASEOUS MIXTURES CONTAINING THEM Filed Feb. 26, 1936 T INVENTOR.

' Chm/e 6'. a 4 f ATTORNEYS Patented Oct. 13, 1936 UNITED STATES PATENT orrics METHOD FOR THE SEPARATION AND BE- COVERY F KBYPTON AND XENON FROM GASEOUS MIXTURES CONTAINING THEM Application February 26, 1936, Serial No. 6555b 4 Claims. (01. 2175.5)

This invention relates to a method and apparatus for recovering the elements krypton and xenon from gaseous mixtures containing them such as atmospheric air or atmospheric air residues from 5 which oxygen or nitrogen or both have been more or less-completely removed previously.

The invention is characterized by the important feature that the primary object is the recovery of krypton and xenon, the separation of oxygen or W nitrogen being merely incidental to the procedure.

The present method has the important advantage of obtaining substantially all the krypton and xenon contained in the sum total of air treated in a very eificient manner. The method is not intended as an auxiliary to air separation methods such as are in common use today for the welding and cutting industry, but is particularly adaptable to cases where exceedingly large volumes of air are treated to obtainthe krypton and xenon in quantities sufficient, for new industrial applications.

Limited quantities of oxygen of 95% purity or higher, even 99.6% purity, may be obtained incidentally without any important additional expense. The method may even be operated in such a-manner as to recover practically all of the oxygen contained in the air treated in such manner.

- Furthermore, another important feature characterizing the present invention is as follows:

First, consider the case where the recove y. ex-

cept in small fractions (0.1 to 0.3) of the oxygen is not desired. In this case more especially, as

hereinafter described, only a small fraction (around 0.1) of the total air treated in the sys- '35 tem is liquefied and since this is true, the compositions .of the vapors to be condensed are not greatly difierent from the compositions of the liquids by thermal contact with which they are condensed. The pressure necessary in order to 40 cause such condensation is relatively small and thus the power requirements in the whole system is also very small.

If larger quantities of oxygen than those indicated above are desired, the pressure difierences 45 between vapors to be condensed and liquids by" which they are condensed increases slightly, but

in all cases these pressure difierentials are so small that they may be produced by compressors of theturbo type. Such compressors, it is well 50 known, are peculiarly adapted to handle exceedingly large volumes of gas such as air if the pressure dilferentialresulting is not too great, say 5 atmospheres;

Further advantageous features of the invention 55 nay be'better understood by references to the following descriptions and the accompanying diagrammatic drawing which illustrates an apparatus suitable for the operation of the invention, particularly as applied to the extraction of krypton and xenon from air. 5 Referring to the drawing, atmospheric air is delivered by a low pressure or turbo compressor 5 and after being cooled in the exchanger system t enters the separation system through pipe l and thence to a coil 8 located at the bottom l0 level of a rectification column 9 wherein it. is liquefied by indirect contact with the liquid collecting at the bottom of column 9. .The pressure necessary to be maintained upon this air is only that required for condensation by indirect con- 15 tact in coil 8 with the liquid Just specified. From coil 8, the air, now in the liquid state, passes through pipe Ill and pressure reducing valve H wherein its pressure is lowered to that prevailing in column 9, after which it is delivered to the 20 top of the column by means of pipe l2.

The liquid then cascades over trays l3 of the rectifier 9 whilethe vapor portion thereof which formed as the result of passage through expansion valve H joins the outgoing waste gas, principally 25 nitrogen, leaving the rectifier through pipe I.

-The column 9 is thus refluxed at the top with liquid air, the krypton and xenon therein contained being found practically wholly-in the liquid portion cascading over trays l3. 3o

. At an intermediate level of column 9 a substantial quantity of unseparated, cooled air is admitted at the pressure of said column. This air is blown through the exchanger-rectification system by a blower (not shown) the pressure required being only that necessary to force it through against pipe friction, etc. The liquid air descending over trays l3 contacts directly with the air entering column 9 through pipe l5, and the krypton-xenon in the air is separated and passes downward in the liquid cascading over trays l3, and

thence to the lowet portion ii of column 9. g

The air liquefied. in coil 8 vaporizes an equivalent portion of the liquid body collecting at the bottom of the column 9 and causes it to ascend through'the column. During this ascent some of the oxygen together with all the krypton, and xenon contentin the total ascending vapor is liquefied and returns with the descending liquid while the residual vapor consisting of nitrogen and oxygen passes out column 9 through pipe M.

The liquid pool collecting at the bottom of column 9 will thus contain a portion of the oxygen and substantially all of the .krypton and xenon contained in the two streams of air admitted into I ously withdrawn through pipe ll controlled by valve II and is delivered to an intermediate level 0! an auxiliary rectifier it. It is in rectifier It that the oxygen contained in the liquid passing through valve II is finally separated from the xenon-krypton concentrate accumulated in the column I. The liquid mixture entering rectifier ll cascades over trays 2. and collects, together with liquid descending from above the level of admision, at the bottom where it submerges.

. with the descending liquid which thus becomes concentrated in krypton and xenon. The liquid descending from above in the rectifier I! is produced partly by condensers 22 and 23 and is partly constituted by the liquid entering the top of rectifier It through valve 3|, this latter liquid being obtained in a manner about to be described.

The liquid passing through pipe 26 and expansion valve 21 to condenser 22 constitutes the krypton-xenon concentrate in its final iorm, being evaporated in coil 22'by producing its equivalent quantity or liquid in the ascending vapors in rectifier it. This condensation and evaporation is advantageously regulated and controlled by means of a suitable vacuum pump after the vapor leaving condenser 22 has passed through the exchanger system and has been warmed up to atmospheric temperature. The oxygen product.

exchanger system is diverted to the coil Ma located at the bottom of rectifier It. An amount of liquid air equivalent to the liquid feed of rectifier it is thus produced in the coil 21a and this liquid leaves rectifier ll through pipe 200 and expansion valve 2! and is added to the liquid air passing through valve ll of the column I and together with that liquid enters the top level of thecolumn. By manipulation of valves 21, 2t

and II, steady conditions with a constant amount oi. evaporation and condensation are maintained in rectifier ll.

Thus far in the description it will be noted that all fluids condensed are liquefied by indirect contact with liquids already formed and thus each-liquidcondensaflon isproduced .by evapv crating an equivalent quantity of'liquid in the thepresentmethodiscarriedoutthatallora portion of the make-up liquid produced by condensation o! vapors by indirect contact with colderyapors shall further the separation while undergoing condensation, for example, I have shown in the dhgram a portion or the cold outgoingnitrogenwastepmductpassingthrougha' coilfllocatedatthetcplevelotrectifier";

the column. A portion or this liquid is continu- This vapor passing through coil 23 has the lowest temperature in the whole system and may advantageously be employed to produce some makeup liquid in the oxygen-krypton-xenon cycle as shown. The quantity of cold gas passing through coil 23 may be regulated by means of pipes II and I2 and valves I3 and 34.

The oxygen eiiluent is withdrawn through a pipe II from the top of the rectifier It and after passing through an exchanger 3 is compressed by a turbo-blower or equivalent compressor 31. It is delivered through a pipe a to an exchanger 39 and thence through a pipe 40 to the coil 2|. A

.portion of the oxygen can be withdrawn through the pipe and valve 42.

The compressor-exchanger system, necessary in order that the various operations constituting the method or the application may be carried out, is similar to that commonly used in the liquefaction of gases and is not, therefore, illustrated in detail.

The method and apparatus as described facilitate the handling of the relatively enormous volume of air which must be treated necessarily to recover krypton and xenon in quantities which would makethese gases available for extended commercial adaptations. As indicated herein, oxygen may be recovered incidentally in a form desirable for commercial purposes, but such recovery is not the primary object of the invention.

Various changes may be made in the details of procedure and in the apparatus without departing from the invention or sacrificing the advantages thereof.

I claim:

1. The method oi separating and recovering krypton and xenon from air whichv comprises liqueiying a portion of the air to be treated, washing a substantially larger volume of air with the liquid air to producea'liquid concentrate containing krypton and xenon in proportions exceeding those present in liquid air, rectifying the liquid concentrate to i'm'ther enrich the liquid in krypton and xenon, and maintaining the low temperature ior the rectification by re-liqueiying the eilluent therefrom and returning the liquid to the rectification zone.

2. The method of separating and recovering krypton and xenon from air which comprises liquetying a portion of the air to be treated. washing a substantially larger volume oi air with the liquid air to produce a liquid concentrate containing krypton and xenon in proportions exceeding those present in liquid air, rectiiylng the liquid concentrate to further enrich the liquid in krypton and xenon and maintaining the low tem perature for the rectification by compressing and liqueiying, the efiluent therefrom and returning the liquid mule rectification zone.

3;lhemethod0tseparatingandrecovering krypton and xenon from air which comprises liqueryingaportionodtheairto be treated, washingasubstantiallylargervolume or airwiththe liquid air to produce a liquid concentrate containing krypton and xenon in propor ions exceedingthosepresentinliquid air,r ectiiyingthe liquid concentrateto further enrich the liquid in krypton andxenon andmaintaining thelowtemperature for the rectification by re-liqueiying the eiluent in heat exchange with the liquid concentrate andreturningthelhmid to therectification '4.Themethodotseparatingandrecovering kryptonandxenoniromairwhichcomprisesu.

liquefying a, portion of the air to be treated, washing a substantially larger volume of air with the liquid air to produce a liquid concentrate containing krypton and xenon in proportions exceeding those present in liquid air, rectifying the liquid concentrate to further enrich the liquid in krypton and xenon and maintaining the low temperature for the rectification by compressing and liquefying the eflluenttherefrom in heat exchange with the liquid concentrate and returning the liquid to the rectification zone.

CLAUDE C. VAN NUYS. 

